How to avoid memory leaks in frame animation?

I've created simple test app with one activity. The activity contains frame animation. The total size of images in frame animation(riffle_forward_anim) is about 1MB. Here is the code I use to load animation:

public class MainScreen extends Activity {
    /** Called when the activity is first created. */

    private ImageView imgForward;
    private ImageView imgBack;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        imgForward = (ImageView) findViewById(R.id.imgForward);

        imgForward.setBackgroundResource(R.anim.riffle_forward_anim);

    }

    @Override
    public void onPause(){
        super.onPause();
        AnimationDrawable anim = (AnimationDrawable) imgForward.getBackground();



        int count = anim.getNumberOfFrames();
        for(int i=0;i<count;i++){
            anim.getFrame(i).setCallback(null);
        }

        imgForward.getBackground().setCallback(null);

        imgForward = null;
    }
}

As you can see I try to release memory in onPause() method. Yes, I've read http://developer.android.com/resources/articles/avoiding-memory-leaks.html

Anyway crash occurs if I change portrait/landscape mode several times. I understand that I can handle orientation change and avoid crash but I need to release memory in my other app without orientation change. That is why I've created simple test app to understand how releasing memory works. Can anyone give me a hint on how to implement 开发者_JAVA技巧this?

Thanks